var name = "window"

var person = {
  name: "person",
  sayName: function () {
    console.log(this.name)
  }
}

function sayName() {
  const ns = person.sayName

  ns() // 默认绑定: window undefined

  person.sayName(); // 隐式绑定: person

  (person.sayName)(); // 隐式绑定: person

  (b = person.sayName)() // 术语: 间接函数引用, window undefined
}

sayName()